FED-STD-228A
Method 1511.1
18 APRIL 2014
LAY OF TWIST, ARMOR WIRE
1. SCOPE
1.1 This method is intended for use in determining the lay of twist (the ratio of the length of lay to the
pitch diameter of the layer of armor wire) of armor wire. The pitch diameter of any layer of wire of a cable
is the diameter of the circle passing through their centers.
2. SPECIMEN
2.1 The specimen should be a piece of the inspection unit of sufficient length to include at least two
complete spirals of the armor wire from which any covering over the armor has been removed.
3. APPARATUS AND REAGENTS
3.1 The apparatus and reagents shall be as follows:
3.1.1 Steel scale graduated to 1/32 inch or finer or its decimal equivalent.
3.1.2 Binding cord or flexible wire.
3.1.3 Wiping cloth.
3.1.4 Alcohol or other suitable solvent.
4. PROCEDURE
4.1 The specimen shall be free from mechanical damage. Any dirt, fibers, saturants or other extraneous
materials shall be removed from the specimen by means of the cloth and solvent. If necessary, the armor
wires shall be secured in their original position by means of binding cord. The distance parallel to the axis
of the specimen in which a helical element of the armor wire makes two complete spirals shall be
measured to the nearest 1/32 inch with the steel scale and the value recorded as 2L.
4.2 The diameter of the specimen over the armor shall be measured as described in method 1221 for
diameter over the armor of the specimen and the value recorded as D1.
4.3 The armor wire shall then be removed from the specimen and any fibers, saturants, or other
extraneous materials removed from the wire by means of the cloth and solvent. The diameter of the
armor wire shall be measured as described in method 1421 and the value recorded as D2.
5. RESULTS
5.1 Calculation. The lay of twist of the armor wire at any place shall be calculated as follows:
Lay of twist = 2L/2 (length of lay)__
D1-D2 (pitch diameter)
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